This invention is directed to controlling the reading and writing of data residing on substantially flat media, and more particularly to controlling the alignment of read/write heads used for reading and writing data on substantially flat media.
Reading and writing data to and from substantially flat media used in magneto-optical storage requires a read/write head configured to xe2x80x9cflyxe2x80x9d above the media on an actuator arm, deriving a signal that is then processed by a preamplifier (also called preamp) mounted on or proximal the base supporting the actuator arm.
In order to find the data, the read/write head must be precisely directed to a xe2x80x9ctrackxe2x80x9d on the substantially flat media on which the data resides. On media where a contrast exists between the data tracks and the xe2x80x9cfieldxe2x80x9d of the substantially flat media; with xe2x80x9cfieldxe2x80x9d being defined herein as those areas between the data tracks in which no data is written; the information allowing precise direction may be derived from reflection data.
As data has become steadily denser and more speed is required, tolerances have become ever closer. This means that precisely directing the head, called xe2x80x9cpositioningxe2x80x9d, is becoming steadily more difficult. Four parameters are often involved in positioning; focus error signal, tracking error signal, reflectivity data signal, and magneto-optical data signal. While all of these are important, it has been found that focus error is very sensitive to various factors tending to degrade performance, such as misalignment, thermal drifts, and wavelength shifts.
One means often used to improve the performance of sensitive functions is the use of the so-called differential amplifier. Differential amplifiers have the advantage over other amplifier types that the differential amplifier need resolve only a small difference between two signal leads, rather than the absolute value of a signal. Additionally, the signal is normally presented on both inputs to the differential amplifier, but with an inverse phase relationship. This may have the advantage of causing the signal strength to be improved.
Unfortunately, the positioning devices of the prior art have not provided a differential signal for applying to a suitable amplifier.
The present invention will be seen to provide a solution to this and other problems, such as the possibility of less cost of a positioning system, due to relaxed absolute values that might be used at a given level of performance.
A differential signal for focus error is provided in a positioning system. A light beam, such as a laser beam, is focussed on a track disposed for maintaining a head position. The head reads and writes data from media through a system including a half-aperture beam-splitter, collimating and focussing system. A reflection, which is directed by the collimating and focussing system back to the half-aperture beam-splitter and focussed with the aid of additional optical processing elements on a novel detector system, develops a differential signal proportional to the focussing error as well as a tracking error signal, reflectivity data signal, and magneto-optical data signal.
Presenting the focussing error signal in differential form provides a more stable and more easily discerned signal whereby higher performance with improved quality is obtained.